The present invention relates to an article for handling small volumes of liquid. More particularly, the present invention relates to an article capable of transferring liquid, on a well-to-well basis, from a source container having a first format or configuration (e.g., a 96-well micro-titer plate, a vial, etc.) to a destination container having a second format (e.g., a 1536-well micro-titer plate).
Advances in the field of combinatorial chemistry, high throughput screening and genomics research have pushed liquid handling capabilities of conventional devices and instrumentation to the limit with regard to high-speed handling of micro-volumes of liquid (i.e., from 0 to about 2 microliters). Specifically, many of the techniques used in such fields require aspirating liquid from and dispensing liquid into micro-titer plates or other containers configured to retain very small quantities of liquid.
Progress in the aforementioned fields is generating a need to miniaturize assay format from, for example, the common 96-well micro-titer plate (6.5 mm well diameter) to 384-well plates (3.5 mm square wells) and to state-of-the-art 1536-well plates (1.3 mm well diameter). With these and other assay formats in use, situations arise wherein liquid must be transferred between plates having different formats. The usual application is transferring liquid from a relatively lower density format, such as a 96-well plate, to a relatively higher density format, such as 384- or 1536-well plates. This transfer of liquid between plates having different formats is referred to as xe2x80x9creformatting.xe2x80x9d
Tools are available for en masse reformatting. En masse reformatting is when the contents of groups of wells or even all the wells of a plate having a first format are transferred, in a single operation, to the wells of a plate having a second format. The devices for doing such en masse reformatting typically use a plurality of syringes (e.g., 8 syringes or 96 syringes are common) that aspirate the contents of the wells of, for example, a 96-well plate, and dispense the aspirated liquid into the wells of higher density plates.
Of late, there has been interest in reformatting on a well-by-well basis. In other words, rather than en masse reformatting, a need has arisen to transfer the contents of a particular well in a source plate to a particular well in a destination plate. The prior art offers little in the way of technology for this application.
One option, at least in theory, for well-to-well reformatting is to reformat manually using a pipette. In practice, this is impractical if not impossible. Aside from an inability to achieve a sufficient throughput rate for commercial scale operation, it is probably beyond the capabilities of a human to accurately or repeatedly pipette liquid into the 1.3 mm wells of a 1536 well plate.
Another solution in the prior art for well-to-well reformatting is to use a single pipette head that is attached to an x-y-z-positioner, such as is described in U.S. Pat. No. 4,979,093 (xe2x80x9cthe ""093 patentxe2x80x9d) assigned to Cavro Scientific Instruments. The xe2x80x9csingle channelxe2x80x9d (i.e., one pipette) arrangement for dispensing that is described in the ""093 patent is depicted herein in FIG. 1.
Arrangement 100 depicted in FIG. 1 includes two variable length arms 102 and 104 that are connected to hinge 106 and to respective pivots 108 and 110. Stepper motors (not shown) that are disposed within pivots 108 and 110 change the length of arms 102 and 104 via friction drive wheels and pinch rollers (not shown). Storage reels (not shown) that are disposed in pivots 108 and 110 accommodate changes in the length of arms 102 and 104. Changing the length of the arms causes movement in the x-y plane.
Receiver 107, which is connected to arms 102 and 104, engages pipette 124. Pipette 124 is operatively connected to z-motion controller 116 via an xe2x80x9cactuator/flow tubexe2x80x9d (not shown) that is disposed within guide tube 114. The actuator/flow tube slides within actuation guide 114 when actuated by z-motion controller 116. Such sliding movement of the actuator/flow tube causes pipette 124 to move along the z-axis (i.e., vertically).
The actuator/flow tube is also connected to fluid dispenser 118. Fluid dispenser 118 is operative to cause pressure changes within the actuator/flow tube. Negative relative pressure enables pipette 124 to aspirate fluid, such as from wells 128 in source plate 126. Conversely, positive relative pressure enables pipette 124 to dispense aspirated fluid, such as into wells 132 in destination plate 130.
Source plate 126 and destination plate 130 are registered in a known position on a stationary platform (not shown). The x-y-z coordinates of any well 128 in source plate 126 and the x-y-z coordinates any well 132 in destination plate 130 can therefore be determined. To aspirate from well 128A in source plate 126 and then dispense the aspirated liquid into well 132-19 in destination plate 130, computer 120 transmits the corresponding x-y-z coordinates of the source and destination wells to controller 122. Controller 122 converts the coordinates into motor control information that drives the motors (not shown) that control the arms 102 and 104 and the z-motion controller 116.
There are a number of shortcomings or problems with the apparatus described in the ""093 patent. In particular, the positioning operation is relatively slow and disadvantageously exhibits characteristically low positioning and dispensing accuracy since all major liquid dispensing functions are operated on a moving, cantilevered liquid carrier (i.e., the pipette).
Moreover, this device introduces inefficiency (i.e., time delays) as a result of the manner in which a series of transfers are effected. That is, liquid transfers are typically sequenced without regard to the relative positions, in successive cycles, of the source and destination wells.
Furthermore, it will be appreciated that the syringe of a reformatter must be washed between dispenses to avoid possible cross contamination. Prior art reformatters and liquid dispensers in general have very inefficient wash cycles. In particular, in such devices, the working pipette is typically transported to and from a wash station, increasing the operating-washing-operating cycle time. Moreover, wash operations require internal and external washing of the working pipette, so that the washing operation creates a substantial waste problem in view of the number of washes involved and the relatively wasteful manner in which wash solution is used.
A need therefore exists for an improved single channel reformatter.
The present invention provides, in some embodiments, a single channel reformatter that avoids the drawbacks of the prior art. In particular, the present reformatter is fast and has very high positioning and dispensing accuracy. Such speed and accuracy is achieved, in part, by disposing the source and destination plates on a x-y stage. Rapid and precise motion is more readily obtained by moving the plates on a x-y stage than by moving a pipette at the end of a cantilevered arrangement as in the prior art.
Moreover, in some embodiments of the present invention, the liquid transfer vehicle (i.e., pipette, syringe, etc.) is limited to z-axis motion and, in fact, is mechanically de-coupled from the x-y stage. A repeatable, accurate dispensing operation is more readily obtained with a syringe, etc., that is stationary in the x-y plane than with one that is moving in three dimensions at the end of a cantilevered arrangement as in the prior art.
In a further embodiment, the present invention provides an efficient wash system that advantageously operates between successive plate-to-plate transfer operations (hereinafter xe2x80x9cnormal liquid transfer operationsxe2x80x9d or xe2x80x9cworking cyclexe2x80x9d). Since, in accordance with the present teachings, the liquid transfer vehicle does not travel in the x-y plane during the working cycle, it can be, and advantageously is, integrated directly into such a wash system. In such an integrated system, no time is lost, as with prior art dispensers, in moving the liquid transfer vehicle to a wash station and back again for the subsequent working cycle.
In some embodiments, the wash system comprises two syringesxe2x80x94a wash syringe and a waste syringexe2x80x94in addition to the liquid transfer vehicle. In such embodiments, the liquid transfer vehicle is advantageously configured as a syringe (hereinafter the xe2x80x9cworking syringexe2x80x9d). The three syringes are in fluidic communication with one another and with supply and waste reservoirs. Further, the three syringes and their plungers cooperate mechanically with a single drive mechanism such that a xe2x80x9cstrokexe2x80x9d of the drive aspirates (dispenses) the working syringe and the waste syringe while, at the same time, the wash syringe is dispensed (aspirated). Moreover, in some embodiments, the drive element that actuates the plungers during the wash cycle is used during normal liquid transfer operations.
The present invention also provides a method for controlling the reformatting operation. The method advantageously comprises: (1) specifying well-to-well links, (2) determining a preferred execution order for executing the specified links thereby enhancing reformatting efficiency, and (3) executing the specified links in the preferred order. In some embodiments, the preferred execution order sequences links based on the relative locations of xe2x80x9cdestination wellsxe2x80x9d (i.e., wells that receive liquid from the source plate) in successive cycles.